1. Field of the Invention
The present invention relates generally to a linear motion rolling guide unit, applied to cutting machines, grinding machines and woodworking machines, and more specifically to a linear motion rolling guide unit with a sealing device easily mounted to the existing machines.
2. Description of the Prior Art
A conventional linear motion rolling guide unit, as shown in FIG. 15, has a track rail 1 having raceway surfaces (raceway grooves) 11 formed on both longitudinal sidewall surfaces 10 thereof and a slider 2 mounted slidable astride the track rail 1. The slider 2 is slidable relative to the track rail 1 and comprises a casing 3 having raceway surfaces (raceway grooves) at positions facing the respective raceway surfaces 11; cylindrical rollers 4 or rolling elements that allow relative movement between the facing raceway surfaces 11 and 12; and end caps 5 attached to the longitudinal ends of the casing 3, the longitudinal direction representing a direction in which the casing 3 slides. The end caps 5 each have an end seal 6 that provides longitudinal sealing between the track rail 1 and the slider 2. The end caps 5 also have a grease nipple 7 for supplying a lubricant to the rolling elements between the track rail 1 and the slider 2 and to their sliding surfaces. A retainer plate 8 is attached to the casing 3 to prevent the cylindrical rollers 4 from coming off the casing 3. An under seal 9 is provided to the undersides of the end caps 5 and the casing 3 to seal gaps between the casing 3 and end caps 5 and the longitudinal sidewall surfaces 10.
When foreign matters such as dirt, dust and chips get into the gap between the track rail 1 and the slider 2 and adhere to the raceway surfaces 11, 12, the smooth running of the rolling elements is blocked. For this reason, the end seals 6 are secured to the end surfaces of the end caps 5 with screws 13 to prevent ingress of foreign matters through the gaps at the end surfaces of the slider 2. Chips, when they are large in size and amount, may cause deformation or even damage to lip portions 14 of the side seals 6 and get into the interior of the slider 2. Thus, when the linear motion rolling guide unit, a precision device, is used under severe working environments where foreign matters produced are large in size and volume, a separate dust protection measure needs to be taken.
Under these circumstances, improvements were made by providing the conventional linear motion rolling guide unit with separate sealing devices other than the end seals 6 to offer double sealing function that will complement the function of the end seals 6.
In a sealing device disclosed in Japan Utility Model Laid-Open No. 48612/1990, for example, the end seal is clamped from both sides by an outer protector and an inner protector both having the similar shape to the end seal and these are secured to the end surfaces of the casing. This arrangement clears a major part of the chips by the outer protector, with small foreign matters, which have slipped through the clearance between the outer protector and the track rail, removed by the lip portion of the end seal. The inner protector, because it is attached to the back of the end seal, can back up the lip portion of the end seal and thereby prevent the lip portion from catching foreign matters and passing them into the interior.
Other sealing devices employed in the conventional linear motion rolling guide units include one in which a double wiper is attached to the end surfaces of the casing to form a hermetically enclosed space between the wipers and the track rail surface and in which a means is provided to introduce a pressurized air into the enclosed space (Japan Patent Laid-Open No. 264923/1994) and one in which an air blowing device is mounted to the outer end surface of the end seal through a spacer, with air outlets of the air blowing device located close to at least the upper surface of the track rail and to the raceway surface (Japan Utility Model 38177/1994).
Because the end seal is in sliding contact with the track rail at all times to remove foreign matters adhering to the track rail, degradation over time of the sealing performance due to wear is unavoidable, making it necessary to replace the worn seal. This in turn has led to growing demands for sealing devices that are easy to mount and remove. Among the sealing devices that address such demands is the one disclosed in Japan Utility Model laid-Open No. 23818/1992. This sealing device has the end seals inserted from under the end caps into the recessed grooves formed at the open end portions of the end caps, allowing one-touch installation.
Although the conventional sealing devices have high sealing capability, their application to the commercially available linear motion rolling guide units such as shown in FIG. 15 raises a problem of having to modify the fundamental specifications of the linear motion rolling guide unit.
Another problem of the conventional sealing devices is that when a seal is damaged or worn, the worn seal cannot be easily removed, nor a new replacement seal installed easily. That is, in replacing the seal, although the worn seal may be broken for removal, a new seal must be inserted from the end of the track rail. Further, simply blowing air from the air blowing device, as with the conventional sealing device, does not provide sufficient dust prevention effects when the linear motion rolling guide unit is applied to the cutting machines, grinding machines or woodworking machines.